He's a decent enough player, but limited. If the intention is to use him in – precisely – a limited DM capacity, he could do well. He's not a poor passer, as such – only, again, limited. He's perfectly capable of breaking up play and releasing the ball effectively to a more expansive midfielder (Herrera) to keep the momentum going.
His weakness, as
@Brwned suggests above, is that he tends to look clumsy and out of place when he has to be a bit more adventurous on the ball (and with his passing options). But ideally you'd have Herrera there as – literally – the middle man between Dier and the attack (Pogba, not least, in more of an AM role).
I think that could work. But I obviously agree with the general idea that we should be able to dig up someone for that role somewhere for less than fifty mill. Dunno who that would be, though – we'll probably end up paying pretty heavily for anyone we go for this window.